In a diesel engine, lubricating oil (engine oil) stored in an oil pan is supplied (fed under pressure) by a lubricating oil supply device, such as an oil pump, for the purpose of lubricating and cooling various parts of the engine. However, in recent diesel engines, advances have been made in lowering the rated engine speed (number of revolutions), due to demands for reduced friction and reduced noise, and the like. In order to achieve high torque from a low engine speed range, turbo supercharging is carried out from low engine speeds, and engine oil is essential not only for lubrication and cooling of the turbo which is activated from a low engine speed range, but also as a special cooling jet for the pistons which are subjected to high torque and which generate heat. For this reason, it has become necessary to supply, from a low engine speed, an amount of lubricating oil which conventionally it has been necessary to supply to the various parts of the engine from the lubricating oil supply device principally in a high engine speed region. In order to respond to this, the ejection flow volume of lubricating oil is raised by increasing the size and supply rate of the oil pump.
On the other hand, with regard to the specifications of the oil pump (gear pump), the ejection pressure and the ejected oil volume are specified with reference to the lowest speed (number of revolutions) of the engine, the oil pump is driven in proportion with the engine speed and the ejection volume of the lubricating oil from the oil pump increases in proportion with the engine speed. However, the flow rate of lubricating oil required for lubrication of the engine is inevitably proportional to the speed of the engine, and in a high speed region of the engine, excess work is generated in the oil pump and the load on the engine is increased. Therefore, a lubricating oil supply device is known, in which the engine speed and the ejection pressure from the oil pump are detected by detection means, whereupon an oil regulating valve is driven on the basis of electric control by a controller (ECU) and a portion of the lubricating oil ejected from the oil pump is relieved, in such a manner that lubricating oil approaching the required volume corresponding to the engine speed is supplied to the respective parts of the engine (see, for example, Patent Document 1).